1. The Field of the Invention
The present invention relates to polyaxial and fixed bone screws and components thereof that can be used for stabilizing adjacent vertebrae of the spine or otherwise fixing to bone.
2. The Relevant Technology
Polyaxial and fixed bone screws (often referred to as pedicle screws) are commonly used in spinal operations for adjusting or stabilizing adjacent vertebrae. For example, in one conventional procedure a first bone screw is screwed into a first vertebra while a second bone screw is screwed into an adjacent second vertebra. A stabilizing rod is then secured between the bone screws so as to fix the adjacent vertebrae relative to each other. Bone screws can be positioned on each side of each vertebra and can be positioned in any number of consecutive vertebrae with one or more stabilizing rods extending between the different bone screws.
A conventional bone screw comprises a threaded screw portion having a collar either fixedly or pivotably mounted on the end thereof. The screw portion is threaded into the bone and the stabilizing rod is received within the collar and secured therein. Other conventional bone screws are used for purposes such as securing a bone plate over a facture, fixing a cranial plate, attaching ligaments, mounting an implant and the like. To be strong enough to handle the stresses placed upon them, the bone screws are typically made of titanium or some other biocompatible metal. Being made of metal allows the doctor to view the bone screws using X-ray photographs during and after implantation.
However, because the bone screws are made of metal, the bone screws block X-rays passing through the body, in effect obscuring adjacent bone and other X-ray viewable internal structures surrounding the area and thereby preventing the surgeon from viewing those structures on an X-ray photograph. The metal bone screws can also disrupt MRI and other types of images. This can limit a surgeon's ability to ensure proper placement of the bone screws and diagnose and treat problems that arise near the location of the bone screws after the bone screws have been implanted.
Accordingly, what is needed are polyaxial and fixed bone screws that overcome some or all of the above disadvantages.